There are many known methods and devices for coating a moving web and other fixed or moving endless substrates, and for smoothing the resulting coating. Several are described in Booth, G. L., “The Coating Machine”, Pulp and Paper Manufacture, Vol. 8, Coating, Converting and Processes, pp 76-87 (Third Edition, 1990) and in Booth, G. L., Evolution of Coating, Vol. 1 (Gorham International Inc.). For example, multiroll coaters (see, e.g., U.S. Pat. Nos. 2,105,488; 2,105,981; 3,018,757; 4,569,864 and 5,536,314) can be used to provide thin coatings. Multiroll coaters are shown by Booth and are reviewed in Benjamin, D. F., Anderson, T. J. and Scriven, L. E. “Multiple Roll Systems: Steady-State Operation”, AIChE J., V41, p. 1045 (1995); and Benjamin, D. F., Anderson, T. J. and Scriven, L. E., “Multiple Roll Systems: Residence Times and Dynamic Response”, AIChE J., V41, p. 2198 (1995). Commercially available forward-roll transfer coaters typically use a series of three to seven counter rotating rolls to transfer a coating liquid from a reservoir to a web via the rolls. These coaters can apply silicone release liner coatings at wet coating thickness as thin as about 0.5 to about 2 micrometers. The desired coating caliper and quality are obtained by artfully setting roll gaps, roll speed ratios and nipping pressures. Another type of coating device is shown in U.S. Pat. No. 4,569,864, which describes a coating device in which a thick, continuous premetered coating is applied by an extrusion nozzle to a first rotating roll and then transferred by one or more additional rolls to a faster moving web.
Devices for coating substrates of limited length (e.g., small sheets) are also available, and can be used to prepare experimental or test coatings without requiring set up or operation of a web coating apparatus. These are commonly referred to as hand spread devices, and consist of a knifing apparatus in which a gap is set between a knifing edge and a bed plate, and a sheet is pulled through the gap while it is flooded with coating liquid. Another example is a wire-wound rod coater known as a “Mayer Bar” (see U.S. Pat. No. 1,043,021 to Mayer) which can be used to make manual hand spreads on small test sheets.